The present invention relates to an electric rotating machine which can be reduced in size by improving the thermal conductivity of an insulating material used therein.
A method of improving the thermal conductivity of a main insulator used in the stator windings of an electric rotating machine is described in, for example, an article entitled xe2x80x9cAn Improved Insulation System for the Newest Generation of Stator Windings of Rotating Machinesxe2x80x9d, CIGTE, 1994 Session, August 28-September 3, 11, 101. In the described method, the overall thermal resistance of the stator windings is reduced by filling the main insulation with fine particles made of an insulation material having a high thermal conductivity, such as alumina. Further, a main insulator formed by adding high thermally conductive particles or a composite of the particles and glass fiber into mica bonding layers is disclosed in Japanese Patent Application Laid-open No.63-110929 and Japanese Patent No. 127364 (1987). Furthermore, an insulation formed by bonding a tape made of mica and glass fiber cloth is disclosed in Japanese Patent No. 411834.
Although the thermal conductivity of a main insulator used in the stator windings of an electric rotating machine has been increased as described above, the overall thermal resistance of the main insulator of the stator windings can not be decreased when the heat load is increased as the electric power generating capacity increases. When the electric power generating capacity is increased, the voltage generated in the stator windings is generally increased and, consequently, the thickness of the main insulator must be increased in order to obtain a required electric insulating property. Particularly, in a case where the breakdown voltage per unit of thickness of the main insulator is low, the thickness of the main insulator increases. Therefore, when an attempt is made to increase the electric power generating capacity while keeping the size constant, the thickness of the main insulator has to be increased, and, accordingly, the machine size inevitably increases.
An object of the present invention is to provide an electric rotating machine which is small in size and low in cost by reducing the necessary thickness and volume of insulation through an adjustment of the breakdown voltage and thermal conductivity of an insulator and an insulation composing the other insulations. Further, another object of the present invention is to provide a method of measuring the thermal conductivity of an insulator under a condition in which the insulator is applied to an electric conductor.
An essential feature of the present invention is that a main insulator used in a stator winding of a rotary electric machine comprises a laminated layer composed of a first insulating layer formed by bonding a thin flake-shaped inorganic insulating material substantially excluding a granular filler with a thermosetting resin and a second insulating layer formed by dispersing a fiber insulating material and a high thermally conductive filler into a resin and curing the resin, wherein the initial breakdown voltage V is set to a value higher than 20 kV/mm, and the thermal conductivity xcex in a thickness direction of the laminated layer is within a range of 0.35 to 1 W/mxc2x7K, preferably 0.5 to 1 W/mxc2x7K, and the product Vxc2x7xcex of the initial breakdown voltage and the thermal conductivity is set so as to satisfy the relationship of 7xe2x89xa6Vxcexxe2x89xa620 (MVW/m2xc2x7K). In order to obtain the above-described thermal conductivity xcex, an insulation satisfying the value Vxcex described above is formed by filling or mixing a granular insulating material having a high thermal conductivity higher than 5 W/mxc2x7K into a resin together with a fiber cloth.
The first insulation layer is formed by bonding a flake-shaped insulating material, such as mica, having a high electric insulating property capable of ensuring a high dielectric strength, with a thermosetting resin. A granular hard insulating material is not added in the first insulation layer so that the insulating material flakes are aligned and bonded in a layer shape and so as to prevent the flake-shaped insulating material from being broken. This point is based on an idea completely different from the prior art described above.
The second insulation layer contains a fiber cloth, such as a glass fiber, or a plastic tape, such as a polyimido film. The fiber cloth is necessary for increasing the mechanical strength of the insulating material layer and for forming the composite laminated body composing the main insulation into a tape. Either woven cloth or unwoven cloth may be employed as the cloth. The granular high thermally conductive insulating material is indispensable for increasing the thermal conductivity of the main insulation tape, and a material having a thermal conductivity higher than 5 W/mxc2x7K, particularly, higher than 30 W/mxc2x7K, is employed as the granular high thermally conductive insulating material. The cloth and the granular or flaky filler are mixed in a thermosetting resin, and the resin is cured.
One or more of the first insulation layer and the second insulation layer are employed alternatively. An amount of the resin is selected so that the thermal conductivity in the thickness direction of the laminated body attains a value higher than 0.3 W/mxc2x7K, particularly within a range of 0.35 to 1 W/mxc2x7K, preferably within a range of 0.5 to 1 W/mxc2x7K. The initial breakdown voltage of the laminated body depends on the amount of the resin being used. When the amount of resin is too small, the initial breakdown voltage of the insulation tape becomes insufficient. When the amount of resin is too large, the thermal conductivity of the insulation tape becomes insufficient. The amount of the resin in the insulation tape is preferably within a range of 20 to 50 weight %.
The insulation used for the second insulation layer may be used as a spacer insulation. The amount of the resin and the amount of the filler are adjusted so that the thermal conductivity of the second insulation layer becomes within the range of 0.35 to 1 W/mxc2x7K, and the initial breakdown voltage becomes higher than 20 kV.
The amount of insulating material added in the resin is adjusted so that the above-mentioned value Vxcex is satisfied, the necessary thermal conductivity is obtained, and the breakdown voltage is not decreased. In the case of a rotary electric machine in which the inside of the rotary electric machine is cooled by hydrogen when the value Vxcex of the stator windings using the main insulation set within the above-mentioned range is used in the electric rotating machine, a ratio of a product of the diameter of the rotor squared and the shaft length of the stator to the electric generating capacity per number of rotations becomes smaller than 40 m3xc2x7rpm/MVA, and the ratio of a product of the diameter of the rotor squared and the length between supports of the rotor to the electric generating capacity per number of rotations becomes smaller than 50 m3xc2x7rpm/MVA. In the case of an electric rotating machine in which the inside of the electric rotating machine is cooled by air, the ratio of the product of the diameter of the rotor squared and the shaft length of the stator to the electric generating capacity per number of rotations becomes smaller than 70 m3xc2x7rpm/MVA, and the ratio of the product of the diameter of the rotor squared and the length between supports of the rotor to the electric generating capacity per number of rotations becomes smaller than 85 m3xc2x7rpm/MVA.
Further, the present invention improves the thermal conductivity of a rotating electric machine by filling or mixing insulating materials having a thermal conductivity higher than 5 W/mxc2x7K into insulators in the rotor, such as a slot insulator, an insulating block or a retaining insulator, or spacers interposed between windings at an end portion of the stator winding. Furthermore, the present invention can be applied to a conductor sheathed with an insulating tape containing a woven inorganic or organic fiber as a base material, and the thermal conductivity of the insulation-sheathed conductor is improved by using such insulating materials.
The main insulation is formed by filling or mixing a granular insulating material and/or a short-fiber insulating material and/or a thin flake-shaped insulating material having a thermal conductivity higher than 5 W/mxc2x7K into a thermosetting resin, a thermoplastic resin or a rubber material, so that the initial breakdown voltage becomes higher than 20 kV/mm and the thermal conductivity becomes within the range of 0.35 to 1 W/mxc2x7K. An insulation having a thermal conductivity within the range of 0.35 to 1 W/mxc2x7K is formed by filling or mixing a fine granular insulating material or a fiber insulating material having a thermal conductivity higher than 5 W/mxc2x7K into a thermosetting resin, a thermo-elastic resin or a rubber, and the insulation may be interposed as a spacer between the windings at the end portion of the stator.
In accordance with the present invention, the thermal conductivity of an object is measured by attaching a heat insulating block onto the measured object formed on a rotary electric machine or the like, and a heating member, such as a heating wire, a film heater or a combination of a wire and a film heater, is attached onto a surface or a local surface of the heat insulating block, whereby the block member is heated by the heating member, and then the change of temperature of the block member is measured.
The high thermally conductive insulation materials having a thermal conductivity higher than 5 W/mxc2x7K usable in accordance with the present invention are boronnitride, aluminum nitride, silicon nitride, alumina, magnesium oxide, beryllium oxide, silicon carbide and the like. Particularly, alumina, boron nitride, and magnesium oxide are preferable because the thermal conductivity thereof is above 30 W/mxc2x7K and the bulk resistance is above 1013 xcexa9cm. These compounds are used in the form of particles having an average diameter smaller than 20 xcexcm. An insulation material containing glass fiber or another organic or inorganic fiber is known, and the fiber is mixed in a resin together with the above-mentioned granular insulation material.
Since a high breakdown voltage is required for the main insulation, the main insulation employs a laminated composite insulation formed by bonding the thin flake-shaped inorganic material with a bonding resin (the insulation shares particularly the withstanding voltage) and an insulation formed by dispersing the fiber and/or particles described above in a resin. In the case where a slightly brittle inorganic insulation material, such as mica, is used for the thin flake-shaped insulation material, the particles and the fiber described above are mixed into the insulation layer as small as possible. If mixed, the thin flakes of mica can not be aligned in a layer shape to decrease the dielectric strength, and the mica may be broken to further decrease the dielectric strength.
An insulation material formed by dispersing a short fiber or particles in the resin is used for an insulation, such as the spacer which requires not so high a withstanding voltage compared to the main insulation. The fiber filler may be in the form of woven cloth, such as a glass cloth, or nonwoven cloth or a short fiber.
In order to maintain the mechanical strength of the spacer, the fiber cloth is necessary. Such insulation may be used by laminating the cloth in plural layers. Particularly, in a case of using woven cloth, such as glass cloth, an insulation having a necessary thickness can be formed by laminating the woven cloth.
The amount of resin in the first insulation layer and the second insulation layer is preferably 10 to 25 weight % of the total amount of the resin and the filler. When the amount of resin is below 10 weight %, the withstanding voltage of the insulation becomes insufficient, though the thermal conductivity becomes high. Since the main insulation of a large capacity electric rotating machine requires a withstanding voltage above 20 kV/mm, the amount of resin is set above 10 weight % in order to sufficiently ensure the dielectric strength.
On the other hand, when the amount of resin exceeds 25 weight %, the thermal conductivity becomes insufficient because of a lack of the high thermal conductive filler, and, accordingly, the machine becomes larger in size due to necessity of increasing the thickness of the main insulation layer. The amount of the resin in the laminated insulation having the first insulation layer and the second insulation layer is preferably 20 to 50 weight % of the total amount of the filler and the resin.
The resins usable in accordance with the present invention are thermosetting resins, such as epoxy resin, unsaturated polyester resin, alkyd resin, polyamide resin and so on, for the main insulation. When the insulation proposed by the present invention is used for a spacer, a thermoplastic resin such as a saturated polyester resin or rubber-like acrylnitrilebutadiene copolymer may be used.
A method of molding the main insulation on the conductor of a electric rotating machine will be described in DESCRIPTION OF THE PREFERRED EMBODIMENTS in detail, though a conventional method may be used.
According to the present invention, since the thermal conductivity can be improved while maintaining a high initial insulating breakdown voltage of the main insulation of the stator winding, the thickness of the main insulation can be reduced and the temperature rise of the machine can be suppressed. Consequently, the machine size can be reduced and the cost can be reduced.